>[If you just want to interpret it, I like strings of RPN tokens and a>simple stack-based interpreter. -John]

John's idea is good. I like strings of prefix tokens instead, because
I think they're easier to debug. Also, avoid going with a binary file
- just output ascii, with a newline at the end of a logical node, and
you can even indent to show tree structure. I mean, to do this in the
file itself.

If you haven't chosen a language for the interpreter yet, may I
suggest Perl? It's great for this kind of thing.